Renal Cell Carcinoma (RCC) is among the most lethal and difficult tumors to treat, particularly when disease has spread beyond the kidney and into the surrounding fascia;even intensive combinations of radio- and chemotherapy are not curative and yield only a modest impact on patient survival. There is a major need for alternative therapeutic modalities. Expression of MDA-7/IL-24 in many different tumor cell types causes growth arrest and apoptosis whereas in non-transformed cells it alters neither cell growth nor cell survival. Previous studies have shown that MDA-7 administered either as a virus (Ad.mda-7), as a purified fusion protein (GST-MDA-7), or in conditioned media, suppressed the growth of tumor cells. In RCC we found that low concentrations of MDA-7 (0.5-1.5 nM) suppressed growth without killing cells whereas higher levels of MDA-7 (>20 nM) suppressed growth and enhanced cell death. Low levels of MDA-7 enhanced the sensitivity of RCCs to several agents that generate free radicals. The anti-proliferative and cytotoxic effects of MDA-7 and free radicals were not observed in primary renal cells. The mechanisms by which MDA-7 inhibits RCC proliferation and interacts with free radicals to kill RCCs are not fully understood. Specific aim 1 will determine whether GST-MDA-7, in a dose-dependent fashion, causes increasing amounts of p38 MAPK activation and JNK1/2 activation, in RCCs, whose signaling is believed to be responsible for cytokine-induced apoptosis at high (>30 nM) GST-MDA-7 concentrations. Additionally, we will prove or refute whether [arsenic trioxide (As2O3) and N-(4-hydroxyphenyl) retinamide (4-HPR)], agents that generate reactive oxygen species, enhance the ability of low GST-MDA-7 concentrations (0.5-1.5 nM) to cause prolonged activation of the p38 and JNK1/2 pathways. Specific aim 2 will determine the mechanisms by which combined treatment of RCCs with PI3 kinase and MEK1/2 inhibitors enhance cell killing by purified MDA-7 protein. Additionally, we will prove or refute whether [arsenic trioxide (As2O3) and N-(4-hydroxyphenyl) retinamide (4-HPR)], agents that generate reactive oxygen species, enhance the lethality of low GST-MDA-7 concentrations by causing inactivation of ERK1/2. Specific aim 3 will determine whether infusion of Ad.mda-7 or MDA-7 protein, into a pre-existing tumor, reduces RCC growth and enhances tumor sensitivity to As2O3 and 4-HPR.